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United States Patent |
5,520,038
|
Clark
,   et al.
|
May 28, 1996
|
Device for manufacturing a groove bearing
Abstract
A moveable cage which has a pattern of holes surrounding and concentric
with a central axis of the cage, and a short hard pin located within the
cage, and movable back and forth between the two ends of the cage. A
single drive device attached to the cage causes both translation and
rotation of the cage. As the cage is advanced and rotated, the interior
pin is caused to move backward and forward as the balls roll over the
surface of the pin, so that the wear on the balls and on the surface of
the interior pin is evenly distributed.
Inventors:
|
Clark; Wesley R. (Santa Cruz, CA);
Jennings; David J. (Santa Cruz, CA)
|
Assignee:
|
Seagate Technology, Inc. (Scotts Valley, CA)
|
Appl. No.:
|
279194 |
Filed:
|
July 22, 1994 |
Current U.S. Class: |
72/75; 72/100; 72/113 |
Intern'l Class: |
B21D 015/00; B21D 019/00 |
Field of Search: |
72/75,100,113
29/898.02,898.13,898.067,557
|
References Cited
U.S. Patent Documents
3924434 | Dec., 1975 | Fulier | 72/75.
|
4866966 | Sep., 1989 | Hagen | 72/113.
|
5265334 | Nov., 1993 | Lucier | 72/100.
|
Primary Examiner: Larson; Lowell A.
Assistant Examiner: Butler; Rodney
Attorney, Agent or Firm: Flehr, Hohbach, Test, Albritton & Herbert
Claims
What is claimed is:
1. An apparatus for manufacturing grooves in the surface of a bearing part
on which said grooves are to be formed, the apparatus comprising a cage
having a circular cage wall with a predetermined wail thickness and an
annular pattern of holes in said wall;
a plurality of spherical balls each rotatably disposed in a respective hole
of said annular pattern of holes in said cage wall, each of said bails
having a diameter greater than said wall thickness and further having a
diameter greater than a diameter of said respective hole in which said
ball is disposed so that said ball cannot pass through said hole; and
a pin located within said cage and having a length less than the interior
opening between interior ends of said cage so that as the cage is rotated
and translated relative to the bearing part on which grooves are to be
formed, said balls protruding through said cage wall engage with said
surface of said bearing, so that said balls smoothly roll in said holes in
said cage and axially couple said surface of said beating part being
grooved to said hardened pin whereby with primary movement of said cage,
the rolling of said balls causes a secondary movement to be imparted to
said pin whereby said hardened balls are constantly maintained in groove
forming contact with said surface of said bearing part.
2. An apparatus as claimed in claim 1 wherein said holes in said cage in
which said spherical balls are located have a lesser diameter at an outer
surface of said cage wall than at an inner surface of said cage wall in
order to capture said balls within said holes.
3. An apparatus as claimed in claim 1 wherein the balls are engaged in said
holes in said annular pattern which is symmetrical about a central axis of
said cage.
4. An apparatus as claimed in claim 2 wherein said holes are generally
spherical in shape although a crown portion of said generally spherical
shape is truncated to allow for protrusion of said balls through said cage
wall.
5. An apparatus according to claim 4 wherein said pin has a length greater
than a distance from an axial location of said circular row of balls to
said either end of said cage.
Description
FIELD OF THE INVENTION
This invention relates generally to hydrodynamic groove bearings formed
with pumping grooves, and more particularly to a device for manufacturing
such a hydrodynamic groove bearing.
BACKGROUND OF THE INVENTION
The present invention relates to a device for manufacturing a groove
bearing having a bearing shaft and a bearing bush with cooperating bearing
surfaces, of which at least one bearing surface is formed with a pattern
of pumping grooves.
A device for forming such grooves has been taught in EPA2292. This device,
shown in FIG. 1 hereof, comprises a hard pin around which a cylindrical
cage is arranged which has one or more annular patterns of holes arranged
symmetrically about the central axis of the cage. These holes are engaged
by hard balls having a diameter larger than the wall thickness of the
cage. The cage and the pin or sleeve are each coupled to a drive
arrangement capable of impressing a translation and a rotation upon the
cage and the pin or sleeve. Thus, the cage and pin or sleeve are
separately translated and/or rotated in order to form the grooves in the
surface of the bearing wall. According to the patent owner's own later
filed U.S. Pat. No. 5,265,334, it has been found that in carrying out the
prior art method the pin or sleeve of the prior art device is subjected to
substantial wear as a result of large Hertzian stresses produced at the
contact surfaces between the pin or sleeve and the balls. The wear
particularly causes deformations of the pin or sleeve surfaces surrounding
and facing the cage, so that the contact surface of the pin or sleeve
becomes irregular resulting in inaccurate groove depth. Therefore, this
same U.S. Pat. No. 5,265,334 disclosed an improvement thereof shown in
FIG. 2 of the present application in which the bearing surface of the
bearing part (which may be a pin or sleeve) includes a continuous groove
which is concentric with the central axis of the pin or sleeve, the groove
extending in a longitudinal sectional plane of the pin or sleeve which
contains the central axis. However, this also results in continuous wear
of a single portion of the surface of the pin resulting in an
unnecessarily short life for the device for making grooves.
SUMMARY OF THE INVENTION
It is an object of the present invention to improve upon the known devices
for forming grooves for a hydrodynamic bearing to minimize the wear.
It is a further objective of the present invention to provide a device
which simplifies making grooves for hydrodynamic bearings which are
regularly spaced and have a consistent depth. To this end, the device in
accordance with the present invention is characterized by a cage which has
a pattern of holes surrounding and concentric with a central axis of the
cage, and a short hard pin located within the cage, and movable back and
forth between the two ends of the cage. A single drive device attached to
the cage causes both translation and rotation of the cage. As the cage is
advanced and rotated, the interior pin is caused to move backward and
forward as the balls roll over the surface of the pin, so that the wear on
the balls and on the surface of the interior pin is evenly distributed. In
this way, the life of the groove making device is prolonged, and the depth
of the grooves being formed is consistent. In other words, as the cage is
driven, in a primary mode, the pin performs exclusively secondary
movements derived from the movement of the cage and the rolling of the
balls over the surface to the groove, ensuring a favorable constant
rolling movement of the balls.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in further detail by way of example
with reference to the drawings in which FIG. 1 is a diagrammatic drawing
of a prior art device used to form grooves in a hydrodynamic bearing
surface;
FIG. 2 is a depiction of a further prior art device for forming grooves in
a surface of a bearing to be formed;
FIG. 3A is a diagrammatic sectional view of a device in accordance with the
present invention for forming grooves in a hydrodynamic bearing; and
FIG. 3B is a sectional view taken along the line B--B of the device shown
in FIG. 3A.
FIG. 3C is a diagrammatic sectional view of an alternate embodiment of the
invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Turning specifically to FIG. 3A, the device of the present invention for
forming the grooves comprises a cylindrical cage 10, a bearing pin 12, and
a plurality of hardened isostatically compressed metal balls 14 arranged
in the cage 10. Balls 14 are specifically engaged in holes 16 (see FIG.
3C) in an annular pattern which is symmetrical about the central axis (as
shown in FIG. 3B). The holes 16 are formed by electroerosion from the
inner surface 18 toward the outer surface 20 of the cage 10 so that at the
outer surface 20, the edges of the holes have a smaller diameter or
opening 22 than the opening 24 at the inner surface. In this way, the
hardened balls which are to be used to form the grooves are captured
within the holes 14 and held in place with only the end surface of the
ball exposed to form the groove.
After the balls are inserted in the cage, a pin of a hardened material 26
which is of a length less than the overall length of the channel 30 formed
in the interior of the device is inserted. The hardened pin, which is
preferably of a carbide material so that the balls may roll over the
surface of the pin for a long period of time without pitting or marring or
otherwise wearing away the surface, is also longer than the distance from
either end stopper 32, 34 of the device to the point near the center of
the device where the concentric row of balls 14 is located. By choosing a
pin of this length, when the cage is coupled to a drive means which is not
shown, and which is capable of impressing a translational and rotational
movement on the cage, the balls also engage the surface of the pin 26 and
provide a secondary movement to the pin. In this way, the wear of having
the balls pressed against the surface of the pin is distributed over the
surface of the pin as the primary movement of the cage creates a secondary
movement of the pin.
To form grooves, the device comprising the pin, the cage and the balls is
translated and rotated through the bearing bush 1, thereby causing bearing
grooves to be formed in the softer material of the bearing bush 1. The
number of helical bearing grooves formed corresponds to the number of
balls used. The pitch of these grooves depends on the ratio between the
translational velocity V.sub.k and the rotational velocity .omega..sub.k
of the cage 10. By varying this ratio, grooves of varying pitch can be
obtained. To form a herringbone pattern which is typical of hydrodynamic
bearings, the direction of rotation may be reversed after completing a
specific distance of travel.
As noted above, in the situation illustrated in FIG. 3, the cage 10 is
driven imparting the secondary movement to the pin 26 and causing rotation
of the balls 14. Alternatively, it is possible to move the bearing bush 1,
and create only secondary movement of the balls 14 and the pin 26 with the
cage being held stationary. It should further be noted that there are
alternative ways of forming and assembling the cage and device, two of
which appear in FIGS. 3A and 3C. For example, it may be desirable to form
the empty cage, and place a large spherical hard carbide ball at one end.
The pin 26 is then inserted, and the opposite end closed after the
insertion of a second ball. In this way, the distance between the location
of the concentric line of groove forming ball and the end of the cage is
easily defined to be less than the length of the pin, although a pin of
any length may be used and the pin and balls may be easily replaced. An
alternative approach appears in FIG. 3C where a hardened ball 34 is placed
at one end of the chamber defined in the cage, and a second end is defined
by a screw threaded stopper 32. In this way also, replacement of the pin
26 and/or the balls 14 as wear occurs for either of these two elements of
the device is easily provided for.
In FIGS. 1 and 2, the reference 1 denotes a bearing bush of a hydrodynamic
bearing whose inner surface 3 should be formed with a groove pattern 3A.
The bearing bush in these, as well as in the preferred embodiment of the
present invention, is immobilized by means not shown; as an alternative,
the groove forming device of the present invention shown in FIG. 3A, 3B
and 3C could be immobilized and drive means attached to the bearing bush 1
to translate and rotate that part.
It is to be noted that the invention is not limited to the embodiments
disclosed herein. Alternatives may occur to a person of skill in the art
who studies the present invention disclosure whereby the scope of the
present invention is to be limited only by the following claims.
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